The pharmacokinetics of Hemiscorpius lepturus scorpion venom and Razi antivenom following intramuscular administration in rat

Hemiscorpius lepturus (H. lepturus) is one of the most dangerous scorpions in Iran. Intramuscular administration (IM) of available Razi antivenom to H. lepturus venom is used by many of Iranian clinicians. The purpose of the current study was to investigate the efficiency of IM route for treatment of envenomed patients by H. lepturus. We compared the pharmacokinetics parameters of venom and antivenom via subcutaneous (SC) and IM administration, respectively. The blood samples were taken at various predetermined time intervals, i.e., 10, 40, 60, 180, 210, 360 and 400min following 5μg (131)I-labeled venom and 5, 10, 40, 120 and 360min following 0.2ml of (131)I-labeled antivenom administration. The radio-iodination was carried out using the chloramin-T method. The results showed that pharmacokinetic parameters of the venom were T(elimination half-life) = 103.25min; Vd/F (apparent volume of distribution) = 14.9ml/kg; Cl/F (total blood clearance) = 0.04ml/kg/min; mean resident residual time (MRT) = 244.3min, and for the antivenom T(1/2) = 628.59min, Vd = 666.66ml/kg, Cl = 0.13ml/kg/min and MRT = 1292min. A comparison of pharmacokinetic profiles indicated that the intramuscular administration was helpful in the referral less than 2hr to clinical centers but not those exceeding 3hr. Overall, the data showed that immunotherapy against H. lepturus stings was likely to be more effective through intravenous administration.